The European Commission said it was concerned that Gazprom abused its market position in the upstream natural gas sector in Central and Eastern Europe.
The commission said Gazprom might be interfering with competition in the regional gas market. It stressed that the opening of proceedings means the commission will treat the issue as a priority and doesn't imply guilt.
The commission said it was examining three suspected violations by Gazprom.
"First, Gazprom may have divided gas markets by hindering the free flow of gas across Member States. Second, Gazprom may have prevented the diversification of supply of gas," a statement read. "Finally, Gazprom may have imposed unfair prices on its customers by linking the price of gas to oil prices."
Disputes between Russia and Ukraine have caused disruptions in European energy markets, most recently in 2009. European consumers get about 20 percent of their natural gas from Russian suppliers, though 80 percent of that runs through Ukraine's gas transit system.
European member states have since courted natural gas suppliers in the Caspian region in an effort to break the Russian grip on the energy sector.